Studies on rechargeable secondary batteries have been actively conducted with the development of portable electronic devices such as cellular phones and notebook computers. Particularly, various kinds of secondary batteries have been developed, such as a nickel-cadmium battery, a lead storage battery, a nickel metal hydride (NiMH) battery, a lithium polymer battery, a metal lithium battery and a zinc-air storage battery. Such a secondary battery is combined with a circuit so as to constitute a battery pack, and charging and discharging are performed through an external terminal of the battery pack.